The invention relates to injection devices of the kind by which set doses are apportioned from a cartridge containing a volume of medicine sufficient for several doses. Such devices are often designated as xe2x80x9cpensxe2x80x9d and may be designed as a pen to be carried by a clip in a pocket the same way as a fountain pen. However, the injection devices need not necessarily have a circular cross section but may have an elongated tubular shape with a more or less rectangular cross section. More specifically the invention relates to a display for such an injection device.
The dose is set by operating a dose setting actuator and the set dose is shown on a display either by a pointer pointing at a number indicating the size of the dose or by a number being presented in a window or on an electronic display.
As the size of the injection device commonly is minimised to make it easy for the user to bring the device with him in a pocket the restricted size of the device sets a limit to the size and thereby to the readability of the numbers in the display.
In EP 327910 a scale shoving numbers up to 18 is provided along a perimeter of the device. A pointer points at this scale and by doses larger than 20 units which are set by rotating the dose setting element more than 360xc2x0, the size of the dose must be calculated by reading and adding the showing on to different scales. The device only allows settings in step of two units, i.e. 10 numbers are printed along the perimeter and the maximum size of each number consequently is smaller than a tenth of the perimeter.
The two-scale reading of the dose is avoided where the numbers are printed along a helical drum surface of which the part carrying the number indicating the set dose is presented in a window as in 608343, however the numbers of steps per turn of the dose setting member still puts a limit on the height of each written number, if the number of steps per turn are low the width of the numbers will be correspondingly small.
In EP 554 996 numbers having a height of up to one tenth of the perimeter of the injection device without any restrictions of the width of the digits of the number is obtained by using a counter having a number drum for each digit, i.e. xe2x80x9c1xe2x80x9d counting drum and a xe2x80x9c10xe2x80x9d counting drum. If wanted a xe2x80x9c100xe2x80x9d counting drum may be added an so on. The numbers on the counting drums may all be up to one tenth of the perimeter of the drum or {fraction (1/10)}xc3x97xcfx80xc3x97d where d isx the diameter of the counting drum which almost corresponds to the inner diameter of the injection device.
If an electronic display is used the mechanical movement of the dose setting parts does not set any limit to the size of the display. However, the mechanically working displays are appropriate especially for disposable syringes as the display may be made from the same materials as are the syringe whereby the syringe may easier be disposed of in a way which is environmentally acceptable.
Consequently it is an object of the invention to provide a mechanical display by which still larger numbers are allowed.
A dose display, in which rotation of a dose setting actuator is transmitted to a display means carrying numbers which are in accordance with the set dose presented in a window in a wall of an injection device, is according to the invention characterised in that it has at least one flexible disk which is driven by the dose setting actuator and which in a band along its perimeter carries numbers which can, depending on the rotational position of the disc, be presented in the window to show a set dose, the disc being deflected to follow an inner contour of the device to attain a cylindrical shape with a generatrix extending in the axial direction of the injection device and perpendicular to the axis of rotation of the disc.
If a disc is folded so that diametrical opposite points of its perimeter just meet, each digit along the perimeter can be made about three times as high as corresponding digits written on a drum having a diameter corresponding to the diameter of the tube formed by the folded disc. If the diametrical opposite edges are allowed to overlap the digits may be still higher.
Two discs may be placed with their axis parallel and in a distance less than the diameter of the discs away from each other so that the discs overlap each other to make it possible to show a two-digit number. In that case the disc overlapping the other must be transparent. Alternatively the overlapping disc can be provided with windows wherein the showing of the digits on the overlapped disk can be seen. However, this construction will weaken the disc.
The discs may be provided with a perforation along a circle concentric with the digit band. This perforation is designed to be engaged by transporting sprockets in order to rotate the disk in accordance with rotation of the dose setting member. The perforation may appropriately comprise a number of holes at least corresponding to the number of digits along the perimeter of the disc.
In a preferred embodiment one foldable disk is fixed to the dose setting element to rotate with this element an the numbers from zero to the maximum dose which can be set are printed consecutively along the perimeter of the foldable disk to be presented in a window to indicate the set dose.